Method of lightweight aggregates production from waste-coal combustion ash

Abstract

Manufacturing lightweight aggregate (LWA) by a sintering technique requires a delicate balance among three conditions: forming sufficient amount of molten liquid phase during sintering; reaching an appropriate viscosity for solid-liquid suspension; and emitting sufficient amount of gas that can be entrapped by the liquid phase to form pores. LWAs were made from low-calcium and high-calcium Waste Coal Combustion Ash (W-CCA) including fly ash and bottom ash. A mass fraction of at least 40% liquid phase for fly ash and 50% for bottom ash is required for a successful entrapment of emitted gaseous phases during sintering. Larger pores were observed in the microstructure of LWA samples made using high-calcium W-CCA in comparison to low-calcium W-CCA. This result was mainly attributed to the high-calcium samples forming liquid phases with lower viscosity values and emitting higher amounts of gaseous phase during sintering than did the low-calcium samples. The gaseous phase was generated by hematite reduction and anhydrite decomposition.

We claim: 
     
       1. A method of manufacturing lightweight aggregate comprising the steps of:
 (a) forming at least a 40% by mass molten liquid phase for lightweight aggregate (LWA) made using a waste coal combustion ash; 
 (b) reaching a viscosity of between 100 Pa·s and 10 7  Pa·s for solid-liquid suspension of the LWA; and 
 (c) emitting a minimum effective gas amount of 0.24% by weight of the LWA to form pores in the LWA during sintering. 
 
     
     
       2. The method according to  claim 1 , wherein step (c) comprises forming pores having a diameter between 1 nm and 3 mm. 
     
     
       3. The method according to  claim 1 , wherein step (a) comprises using fly ash. 
     
     
       4. The method according to  claim 3 , wherein the step of providing the LWA comprises providing low calcium fly ash. 
     
     
       5. The method according to  claim 4 , wherein the step of providing the low-calcium fly ash comprises using waste fly ash. 
     
     
       6. The method according to  claim 3 , wherein the step of providing the LWA comprises providing high-calcium fly ash. 
     
     
       7. The method according to  claim 6 , wherein the step of providing the high-calcium fly ash comprises using waste fly ash. 
     
     
       8. The method according to  claim 1 , wherein step (a) comprises using bottom ash. 
     
     
       9. The method according to  claim 8 , wherein step (a) comprises forming between 50% and 100% liquid phase for bottom ash LWA. 
     
     
       10. The method according to  claim 8 , wherein step (b) comprises the viscosity reaching between 100 Pa·s and 10 6  Pa·s for the solid-liquid suspension. 
     
     
       11. The method according to  claim 8 , wherein step (a) comprises using low-calcium bottom ash. 
     
     
       12. The method according to  claim 8 , wherein step (a) comprises using high calcium bottom ash.